how to determine suitable LEDs?

[aethyr]

I'm a newb, trying to learn as much info as I can before I embark on building my own saber.

One thing I noticed in my reading of this forum is that often times a particular LED will be deemed unsuitable for sabers. I can understand if their efficiencies are not very good, ie lumens/watt. You clearly want the most efficient, right?

So then why wouldn't this led be suitable? Granted its only white, but 430 lumens at 350mA is pretty good, no? I've seen posts about a P7 that produces 900 lumens at 3000mA. But that cree led I linked to is way more efficient. Is light output linearly additive? Can I put 3 430 lumen leds together to get over 1200 lumens at 1000mA? Or even just 2 together to get 860 lumens at 700mA is darn good, no?

The other things I would imagine are factors are heat, but as a corollary to efficiency, the more efficient a led is, the less heat it should produce right?

So what other considerations are there for determine whether a particular led is suitable?

[Sunrider]

Hey why lose all those lumins through a color filter. At the same size is the all powerful ssr-90. 2000 colorful lumins. Boyaca

http://www.luminus.com/content1517

[cardcollector]

well, do you want it for a filter?

or for a white blade? The seoul p4 white is my personal favorite with a white blade.

If you are planning to use a filter, I would suggest you find a RGB alternative...

[aethyr]

Oh, I just picked a led that seemed to have really good efficiency. I wasn't attached to the white. But it seems to me, if you could have a very efficient white led, then why not use a filter?

That SST-90 seems like it would need all 9000mA to get 2000 lumens. Thats a lot of juice. I believe with the 900 lumen P7, people were struggling to come up with "just" 3000mA.

My quick research shows that lumens are linearly additive. So two 430 lumen leds is equivalent to a single 860 lumen led. So using my cree led I found, you only need 700mA to hit 860. And at merely 1400mA (less than 1/2 the juice to power the P7), you get 1720 lumens, which is almost twice the light output of the P7. So that cree led is 4x more efficient than the P7 and over 5x more efficient than the SST-90.

What am I missing?

[Sunrider]

The cree is efficient but if you put a filter on it besides yellow you will lose 2/3rds of the lumens. The ssr-90 is bad at the upper end but at 3 or 4 amps way more lumens than the rest.

[FenderBender]

It isn't just the LED, its what power it needs and can you fit that power solution in a hilt. Its also about heat management, the single greatest killer of LEDs. Also efficiency is determined by its optics solution. Can you get all those lumens up the blade tube? We have this problem with the tri-rebels, lots of power/lumens, but can't find a great optics solution to get it all up the blade tube.

[Rhyen Skytracker]

The main issue with the LED you specified is the voltage requirements. You have to keep in mind you don't have much room for batteries. With the batteries you not only want to look at the voltage, but you also want to look at the mAH. That will determine the run time. The Li-Ions will give you higher voltage and the NiMH will give you higher mAh for the same sized batteries. We like to keep the voltages around 4.8 V - 7.4 V. Anything higher than that and you will have problems fitting them in a normal sized saber hilt.

[aethyr]

It isn't just the LED, its what power it needs and can you fit that power solution in a hilt. Its also about heat management, the single greatest killer of LEDs. Also efficiency is determined by its optics solution. Can you get all those lumens up the blade tube? We have this problem with the tri-rebels, lots of power/lumens, but can't find a great optics solution to get it all up the blade tube.

Ah optics. Can you elaborate on this? Is optics merely the case of focusing the beam in a straight line up the tube, sort of like the parabolic reflector on flashlights? Or is there more than this? Are the leds so different than you need different optics for each one? I mean, if I recall my math correctly, for a parabola, its a matter of putting the led at the focii, right?

The main issue with the LED you specified is the voltage requirements. You have to keep in mind you don't have much room for batteries. With the batteries you not only want to look at the voltage, but you also want to look at the mAH. That will determine the run time. The Li-Ions will give you higher voltage and the NiMH will give you higher mAh for the same sized batteries. We like to keep the voltages around 4.8 V - 7.4 V. Anything higher than that and you will have problems fitting them in a normal sized saber hilt.

Ok, so that cree led I posted requires 12 volts, so that is too high? Is it really that hard to find a battery solution that provides 12V with decent amp*hours that fits in the hilt?

So I found these "gumstick" batteries: linky
They are 0.22 inches thin, 0.6 inches wide, and 2.6 inches long. 10 of them together produce 12V with a total of 14000mAh of capacity and take up less volume than 4 AA batteries. They are extremely expensive and 10 of them will set you back $100, but the solution to voltage does exist.

Now back to the filter issue. At 430 lumens each, lets say we install 5 of them, for a total of 2150 lumens. Lets say we throw a filter and lose 2/3 of the lumens. That still gives us 716 filtered lumens at only 1750mA of consumption. The gumstick batteries can provide 12V and plenty of amp*hours.

The other issue is focusing the light beam...I don't have a solution to that yet, but what if I just yanked a suitable flashlight reflector?

[Rhyen Skytracker]

You won't find too many people who will spend $100 for batteries for 1 saber. I know I wouldn't. Price is a concern for these too. Parts and electronics for sabers can add up very quick.

[Sunrider]

Ok three of those batteries would be 16 x 15mm square. To fit even 9 in a mhs hilt you would need 165mm or 8 inches of hilt for only batteries.

The deal with the lens is it focuses the light through a 6 to 10mm aperture into a narrow beam so the led has to fit directly under the small hole. The led must also be centered with the 10mm hole so only one led can be used. Even multi die leds like the mce suffer from not being directly centered with the lens. Reflectors don't make a narrow enough beam.

Check out the Rebles you can get 200 or 300 lumens from them.

If you wan't a higher power challenge the nice thing about the ssr-90s is the light is well distributed across the led with more junctions to produce more light.

The most power dense batteries right now are the 18650s.